External beam radiotherapy (EBRT) is widely accepted as a curative treatment modality for localized prostate cancer. See, for example, Holupka et al, “Ultrasound image fusion for external beam radiotherapy for prostate cancer,” Int. J Oncology Biol. Phys., 1996:35:975-84. However, in order to cure localized cancer of the prostate with radiotherapy, a high dose is needed. Different escalation schedules are used world wide. Generally, it is desirable to decrease the target volume while employing high radiation doses and to use markers in the prostate to increase the positioning accuracy of the target volume. There are, however, radiation dose limitations that should be followed in order to avoid complications in dose sensitive organs, including, but not limited to, the rectum, the bladder and the hips.
Another approach for treatment of prostate cancer is the use of low dose rate brachytherapy, seeds, or 3D conformal radiotherapy combined with a boost of high dose rate (HDR) brachytherapy. See, for example, Åström et al, “Long-term outcome of high dose rate brachytherapy in radiotherapy of localized prostate cancer,” Radiother. Oncol., 2005:74:157-61. Intensity Modulated Radiotherapy (IMRT) has improved the conformality of the treatment delivery and improved clinical outcomes with regard to the delivery of external beam radiotherapy, as described by Mangar et al, “Technological advances in radiotherapy for the treatment of localized prostate cancer,” Eur. J Cancer, 2005:41:908-21.
Proton treatment of the prostate is also employed, either as a single treatment modality or in combination with conventional radiotherapy. Mock et al, “Comparative treatment planning on localized prostate carcinoma conformal photon-versus proton-based radiotherapy,” Strahlenther Onkol., 2005:181:448-55, have reported that the advantageous dose distribution of proton beam radiotherapy for prostate cancer may result in reduced side effects compared to IMRT. With a single perineal proton beam, it is possible to reduce the volume of the rectal wall included in the high dose region as compared with conventional X-ray radiotherapy, Benk et al, “Late rectal bleeding following combined X-ray and proton high dose irradiation for patients with stages T3-T4 prostate carcinoma,” Int. J Radiat. Oncol. Biol. Phys., 1993:26:551-7.
One conventional radiotherapy treatment of localized prostate cancer employs a combination of 3D conformal radiotherapy, with either HDR brachytherapy or a proton boost. The external photon treatment is given in 25 2 Gy fractions, the brachytherapy with two 10 Gy fractions and the proton beam treatment with four 5 Gy fractions. The proton treatment is given with high precision, using gold markers, and the dose to rectum is typically considerably less as compared with EBRT techniques. The rectal toxicity is similar to the combination treatment with EBRT and HDR brachytherapy. The close relationship between the prostate and rectum, however, typically demands a compromise between dose to target and organ at risk. The positioning of the prostate during radiotherapy is also important, since the prostate is known to move in the transversal or craniocaudal direction. Additionally, an internal rotation and tilt angle sometimes occurs which cannot be corrected, even by use of markers in the prostate.
High-precision radiotherapy techniques enable the delivery of dose distributions of increasing conformality relative to the target volume and surrounding critical tissues. In turn, such treatments have become increasingly sensitive to setup error and organ motion, as described by Mechalakos et al, “Time trends in organ position and volume in patients receiving prostate three-dimensional conformal radiotherapy,” Radiother Oncol., 2002:62:261-5. Often, however, treatment of prostate cancer with high-dose radiotherapies is not sufficient due to the close relationship between other organs, and specifically, the rectal wall and the prostate. Thus, a need exists for improved methods and systems for treatment of prostate cancer and for treatment in general of target areas in the vicinity of the rectum.